Process for bleaching off-color cottonseed oils



United? States Patent fice 3,036,102 Patented May 22, 1962 3,036,102 PROCESS FOR BLEACHING OFF-COLOR COTTONSEED OILS Walter A. Pons, Jr., and James C. Kuck, New Orleans, and Vernon L. Brampton, Metairie, La., assignors to the United States of America as represented by the Secretary of Agriculture N Drawing. Filed Aug. 15, 1960, Ser. No. 49,804 1 Claim. '(Cl. 260-424) (Granted under Title 3'5, US. Code (1952), sec. 266) A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to a novel process for the bleaching of refined cottonseed oils to remove fixed red color bodies from oif-grade or unbleachable cottonseed oils in order to produce oils of acceptable color values without producing deleterious efiect on the characteristics or the keeping quality of the oils.

Refined cottonseed oils are customarily treated with adsorbents for the purpose of removing oil-soluble coloring matters which remain in the oil after the usual alkali refining treatment of crude oils. The process is one of adsorption, and is commonly referred to as adsorption bleaching, or bleaching. Adsorbents for this purpose are generally various types of naturally occurring clays which have the property of adsorbing coloring matter from oils. These are used either in the natural state or after suitable activation with mineral acids, and are commonly referred tcdas natural or activated bleaching earths.

In the cas ebf cottonseed oil, reactions which occur between gossypol, the principal pigment of the seed, and other seed constituents, yield red color bodies which are not removed from the oil by alkali refining and bleaching techniques normally applied to cottonseed oil. Oils in which such color bodies occur are referred to by the industry as off-colored or unbleachable defined oils.

The presence of these color bodies in refined cottonseed oils constitutes a serious problem in the cottonseed processing industry since darkly colored oils are discriminated against. In an effort to improve the color of these unbleachable oils, drastic alkali re-refining has been widely used by the cottonseed industry. The drastic conditions used result in increased loss of oil due to saponification by the alkali and to oil entrainment in the soapstocks. in addition dual refining imposes an added cost to cottonseed processing. Moreover these drastic conditions are not fully effective, since in many cases the red fixed color bodies are not removed by re-refining.

A primary object of the present invention is to provide a novel bleaching process for the removal of fixed red color bodies from refined off-colored or unbleachable cottonseed oils.

Another objective is to provide a novel bleaching process for the removal of easily bleachable pigments from refined cottonseed oil.

Another objective is to provide a bleaching process to produce finished cottonseed oils in which the characteristics and the keeping quality are comparable to those of refined and bleached oils produced by conventional methods.

Another objective is to provide an activated alumina adsorbent which, under certain conditions of use, removes the fixed color bodies from elf-colored or unbleachable cottonseed oils.

Another objective is to provide a process for bleaching oif-colored or unbleachable oils and which is adaptable to use with conventional plant equipment customarily employed for the bleaching of vegetable oils.

Crude cottonseed oils obtained from mechanical pressing or solvent extraction of cottonseed are usually treated in commercial operation with suitable concentrations of aqueous alkali to remove from the oil the major portion of the nonglyceridic constituents such as fatty acids, resins, phosphatides and various ill defined mucilaginous substances. Cottonseed oils treated in this manner are commonly referred to in the trade as refined oils. Refined oils contain varying amounts of poorly defined alkaliinsoluble pigments.

In order to produce oils of acceptably low color values, refined cottonseed oils are treated commercially with adsorbents such as fullers earths and bentonites to reduce the concentrations in the oil of pigments which are not removed in the refining process. This process is referred to in the trade as the bleaching process. Fullers earths and bentonites, variously treated, are referred to hereinunder as natural or acid activated bleaching earths.

As customarily performed in the industry, bleaching is conducted on either a batchwise or continuous basis. In the batchwise system the appropriate quantity of fullers earth or bentonite, is mixed with the oil and the resulting mixture is heated to a temperature ranging from about C. to 140 C. The temperature selected depends upon the type of oil and adsorbent, and on whether the system is exposed to the atmosphere or if it is under vacuum. The heated adsorbent-oil mixture is stirred for periods of time necessary to establish equilibrium, usually 20-40 minutes. The adsorbent is then removed by suitable filtration or centrifugal methods.

In the continuous bleaching system, oil and adsorbent are mixed, heated, and separated by filtration on a continuous basis inclosed systems under vacuum.

In the instant invention, 100 parts of refined cottonseed oil are mixed with 1-6 parts of activated alumina comminuted to pass a 400 mesh screen and which contains at least 10% by weight of moisture. The mixture is then stirred mechanically and heated to a temperature of about 225 C. as quickly as practical and held at this temperature for 5-30 minutes. about C. and the adsorbent is removed by a suitable filtration method. The entire operation consisting of heating and filtration can be conduct-ed under prevailing atmospheric conditions, under an inert atmosphere such as nitrogen, or under vacuum.

Activated aluminas are a porous form of aluminum oxide of high surface area and are produced commercially by controlled calcination of hydrates of aluminum oxide. As usually employed, activated aluminas are essentially anhydrous and are widely used in the form of large granules, rods, or spheres, as desiccating agents for gases and liquids, and they are used in various granular states as catalysts for a variety of chemical reactions. These materials are produced by numerous manufacturers and are readily available. We have found, however, that as usually produced, these activated aluminas are relatively The mixture is then cooled to 3 inefficient for removing fixed red pigments'from olfcolored cottonseed oils. They are only efiicicnt when utilized under the conditions set forth in the instant invention. Additionally we have found that common forms of aluminas such as calcined and hydrated aluminas, aluminum hydroxide and aluminum silicate are markedly less effective than activated aluminas for the bleaching of cottonseed oils.

'The relative eificiency of various types of aluminas for bleaching of an off-colored refined cottonseed oil are illustrated by the results shown in Table I Where the color indices recorded are those obtained by the method of W. A. PODS, J. C. Kuck, and V. L. Frampton, Color Index for Cottonseed Oils, in press Journal of the American Oil Chemists Society, 1960. This color index is the area under the optical density-wave length curve in the region of 400550 millimicrons. High quality refined and bleached cottonseed oil have color indices of 15-30 according to this method of estimatingcolor indices. Samples of oil were bleached in accordance with the operational procedure set forth in the instant invention. Three types of commercial activated alumina, commercial cal cined and hydrated alumina, pure aluminum hydroxide, and synthetic aluminum silicate were used. For com parison purposes the oil was also bleached with both natural and activated bleaching earths, adsorbents which are customarily used to bleach vegetable oils. The data set forth in Table I demonstrate that activated aluminas are superior to conventional bleaching earths, to aluminum salts and to calcined and hydrated aluminas for the bleaching of oil-color refined cottonseed oil.

TABLE I Bleaching conditions 1 Adsorb- Moist- Bleach- Adsorbeut ent ture ing con- Particontem- Oil centraole size tent, peracolor tion, (Mesh) perture,. per- 7 cent C. cent None-Refined nil 124. 8 Natural bleaching earth 4. 120 62. 3 Activated bleaching earth. 4. 0 120 52. 8 Aluminum hydroxide 4. 0 225 80. 9 Aluminum silicate--- 4. 0 225 51. Calcined alumina. 4. 0 225 66. 9 Hydrated alumina. 4. 0 225 52. 9 Activated alumina #A 4. 0 225 46. 1 Do 3 4.0 225 33. 4 Activated alumina #B 4. 0 40[) 13. 2 225 32. 8 Activated alumina #0 4. 0 400 22. 9 225 28. 0

1 5 minute contact time at specified temperature. 9 Microns. 3 Air equilibrated.

We have found that theefifectiveness of activated alumina as a bleaching agent is also dependent on its moisture content, on the particle size of the adsorbent and the temperature of bleaching. The effectof contact time of the adsorbent is not critical. The importance of the first three variables, and the effect of each when the other two are held constant is illustrated by the data set forth in Tables II and III. It may be noted from the data (Table II) that when the amount of adsorbent, particle size, moisture content and contact time are held constant, optimum color reduction is attained at bleaching temperatures of 225 'C. or higher. To avoid damage to the oil it is preferred to conduct bleaching at no higher than 225' C.

The efiect of varying the moisture content ofthe alumina when the variables of adsorbent concentration, particle size, bleachingtemperature and contact time are held constant (Table II) indicates that alumina adsorbents are most efficient when the moisture content is at least 10% by weight.

4 TABLE 11 Efiect of Bleaching Temperature, and Moisture Content of Alumina on Bleaching Efiiciency of Activated Alumina.

Variable temperature Variable moisture Bleaching Moisture tempera- Oil color content of Oil color ture, C. alumina,

percent 26 74. 7 Dry 46. 1 75 66. 5 1. 41 47. 1 64. 4 4. 69 40. 7 64. l 5. 64 37. 7 200 48. 0 6. 72 37. 0 225 31. l. 10.42 33. 7 260 30. 1 I3. 36 32. 6

1 4% alumina (-400 mesh) containing 10.4% water in each bleach, 5 minute contact time at designated temperature.

4% alumina (-325 mesh) of designated moisture content in each bleach; 5 minute contact time at 225 0. in each case.

When the moisture content, amount of adsorbent, contact time and bleaching temperature are held constant, and the particle size of the alumina is varied, results shown in Table III demonstrate that the effectiveness of activated alumina in removing red fixed color bodies from off-colored or unbleachable oils increases with the degree of subdivision of alumina particles. We prefer to use 400 mesh alumina, since filtration difiiculties are encountered with more finely divided material.

TABLE III Efiect of Particle Size and Bleaching Time on Bleaching Efi'iciency of Activated Alumina Variable particle size Variable bleaching time Contact Mesh range of activated Oil color time at 011 color alumina 1 225C min.

as. 2 s 31.1

ti 1 4% alumina oi designated particle size in each bleach; 5 min. contact id iiiimiia (-400 mesh) containing 10.4% water in each bleach; designated contact time at 225C. in each case.

The contact time of the adsorbent is not critical, as the data shown in Table III indicate that variation from 5 to 25 minutes has nomarked effect on the color index of the bleached oil. The short contact time required, less than 5 minutes, indicates that the bleaching process is adaptable to continuous bleaching, where oil and adsorbent are continuously mixed, heated and filtered.

The amount of activated alumina used in the bleaching of oif-colored oils depends on the amount of color reduction desired.

Actually, the adsorption of the red color bodies on activated alumina follows the Freundlich adsorption isotherm, and the red color intensity of the bleach oil decreases with increasing quantity of alumina used.

From the data set forth in Table IV where the quantity of natural and acid actuated bleaching earth and of activated alumina is varied from 1 to 6 percent of the weight of the oil in the bleaching of a sample of offcolored refined cottonseed oil, it can be seen that 2 percent of activated alumina produces greater color reduction than 6 percent of conventional bleaching earths.

We have found that the oil entrainment on activated alumina is comparable to that observed for the conventional adsorbents such as natural bleaching earth.

We have also found that the recovery of adsorbed or retained glycerides from the spent alumina adsorbent,

and the re-activation of the adsorbent for repeated use are readily accomplished. Neutral glycerides retained by the adsorbent are approximately 25 percent of the weight of the adsorbent, and are readily removed by solvents such as commercial hexane. The recovered oil, after solvent removal, is of a quality comparable to the alumina bleached oil recovered by filtration.

Strongly adsorbed materials such as fatty acids and color bodies are not removed by solvent extraction. These are oxidized by heating the spent adsorbent to 550600 C. in the presence of air. After equilibration to the optimum moisture level, the regenerated adsorbent is suitable for reuse as a bleaching agent. The reactivation process can be repeated indefinitely.

TABLE IV Efiect of Adsorbent Concentration n Bleaching of Off-Color Refined Cottonseeld Oil Commercial grade, standard AOCS bleach test.

'-Commercial alumina ground to pass a 400 mesh screen, equilibrated to 22.9% moisture. minute bleaching time at 225 C. in each case.

The following examples are illustrative of details of at least one method of practicing the invention.

EXAMPLE 1 Seven samples of refined oil-colored cottonseed oils were used in these experiments.

To 100 parts by weight of each of the seven oils (Table V) were added 4 parts of a commercial activated alumina which had been ground to pass a 400 mesh screen and which contained 17.6 percent water. Each oil and alumina mixture was stirred continuously under prevailing atmospheric conditions, and the mixture was heated rapidly to 225 C. The mixture was held at 225 C. for 5 minutes, cooled to about 75 C. and filtered.

Portions of each refined oil were also bleached by following the operational procedure of the American Oil Chemists Society Official and Tentative Methods where fullers earth (Oificial AOCS earth for 1960) was used.

The color indices of the bleached oils were determined and are recorded in Table V. In all cases improvement in color of the oils bleached with alumina was much greater than that obtained with f-ullers earth.

TABLE V Improvement in Bleach Color of Ofi-Colared Refined Cottonseed Oils by Use of Actzvated Alumina Bleaching Bleach color Refined Oil Type of refined oil-colored oil N 0 cottonseed oil color A.0.0.S. Activated bleach alumina test 1 bleach 2 EXpeller 219 82. 4 56. 9 Screw-pressed- 125 62. 3 30. 2 Rte-refined, expeller 171 48. 3 35. 9 Expeller 104 46.3 30.6 Screw-pressed 130 52.6 31. 5 6 o 147 56.5 28.8 7- Under-refined, screw-press 134 26.5 19.9

1 Ofiicial bleaching test of American Oil Chemists Society. 2 Commercial activated alumina ground to pass a 400 mesh screen, equilibrated to 17.6% moisture. 4% alumina in each bleach, 5 minute contact time at 225 C 0 EXAMPLE 2 A sample of a refined unbleachable oil-colored cottonseed oil, anda sample of refined prime bleachable grade cottonseed oil were each bleached with 4 percent activated alumina as outlined in Example 1. They were then deodorized by use of laboratory scale deodorization equipment. For control purposes, oils were also bleached with 4. percent natural bleaching earth as described in the official and tentative methods of the AOCS and were also subjected to the identical deodorization technique. The results shown in the following table illustrate that there is a reduction in color index on deodorization of both oil-color and bleachable cottonseed oils. This reduction in the color index due to deodorization conditions is well known in the trade. The results demonstrate that for oil-color oils, the reduction after conventional bleaching is not sufficient to produce oils of desirably low color.

The results for Oil B, a bleacha ble oil, demonstrate that activated alumina is also effective for bleaching oils of this type. Although the invention is primarily designed to improve the color of ofl-color or unbleachable cottonseed oils, it may, if desired, be applied also to easily bleachable refined cottonseed oils to produce oils having color values comparable to those obtained by use of conventional adsonbents.

Example 2.Efiect of Bleaching and Deodorizazion 0n Cottonseed Oil Color Natural earth Activated alumina Type of refined cottonseed oil Bleach Deodorized Bleach Deodorized color color color color A. Oil-color 57.8 45.4 35.8 28.3 B. Bleachable 14.3 7.0 15.8 5.1

EXAMPLE 3 A single sample of refined cottonseed oil was bleached Example #3.-Efiecz of Bleaching on Oil Properties Bleached oil Refined Activated alumina Oll property oil Natural bleach only bleachin earth bleach Atmos Vacuum pheric bleach bleach Iodine number 104. 5 104. 7 104. 4 104. 4 Refractive index N13 (3.... 1.4698 1. 4699 1. 4700 1.4699 Unsaponifiable matter, percent 0. 57 0. 53 0. 59 0. 55 Tocopherols, percent 0.053 0.055 0. 056 0.056 Keeping time, hrs. 22. 5 36.0 40. 5 35.0 Absorptivity:

233 mu (diene conjugation 0. 400 0.255 0.681 0. 570 268 mu (triene conjugaon 0. 019 0.222 0.115 0.076 315 mu (tetraeno con gation) 0.0015 0.0083 0.0083 0.0065

Oven stability at 0.; time in hrs. for oil to reach peroxide Value of 100.

The results of the analysis of the oil, as recorded in the accompanying table, indicate that the alumina bleaching technique has no adverse effect on oil properties. Compared with the properties of the oil bleached with conventional bleaching earth, the "unsaturation (iodine num- :-ber, and refractive index), antioxidants (tocophero-ls),

keeping time, and fatty acid conjugation (diene, triene, and tetraene conjugation) of the alumina bleached oil are equivalent. In addition, the properties of the oil bleached with alumina under atmospheric conditions are essentially equivalent to the alumina bleaching conducted under vacuum. Thus the efiect of atmospheric oxidation is not'significant for -the alumina bleaching technique, and the process is adaptable to either batchwise bleaching under atmospheric conditions or to continuous bleaching under vacuum. 4 a

We claim:

A process for bleaching refined ofl-co-lor cottonseed oil comprising treating the refined ofif-color cottonseed oil at :a temperature of about 225 C. with activated alumina comminuted to pass a 400 mesh screen, said activated alumina containing at least 10% by Weight of moisture,

References Cited in the file of this patent UNITED STATES PATENTS Baylis Aug. 27, 1927 2,292,822 Clay-ton Aug. 11, 1942 FOREIGN PATENTS 7 707,454 Great Britain Apr. 21, 1954 

